With the improvement of people's living standards, environmental management of enterprises has been paid more and more attention, and metallurgical enterprises are no exception. At present, there are two kinds of dust collectors used for dust control, and bag filter is still the mainstream of application. Bag filter is widely used in iron and steel industry, from ore crushing, screening, belt transportation, sintering, ironmaking, steelmaking, steel rolling, ferroalloy smelting, coking, lime, refractories, etc., basically every process in the production process can be used and the effect is good.

Bag filter is an efficient dust removal equipment to control air pollution. Bag filter has the highest dust removal efficiency. In China, we will implement the strategy of sustainable development, vigorously strengthen environmental protection, control the total amount of pollutants, and achieve two standards with one control. Bag filter will do a lot in controlling dust, smoke, carbon dioxide, dioxins and other pollution. The biggest disadvantage of bag filter is the need to replace the filter bag. In the past, due to the lack of variety of filter materials, poor quality and poor seam wrapping technology, the dust removal system had a relatively short bag changing cycle, which increased the operating cost and maintenance workload and brought inconvenience to users. Now, there are more and more kinds of filter materials in China. At present, it has been able to produce chemical fiber woven fabric, room temperature needled felt, antistatic needled felt, oil-proof and waterproof needled felt, high-temperature resistant and corrosion-resistant needled felt, glass fiber continuous cloth, glass fiber needled felt and other filter materials with excellent performance suitable for various working conditions, as well as PTFE coated filter materials. The sealing technology has also been greatly improved, and the life of filter bag has been increased to more than 2 years, or even longer, which meets the requirements of users. Therefore, the bag filter will develop rapidly in the future.

Metallurgical dust removal technology and equipment

1 Difficulties in metallurgical dust control

The main sources of dust emitted by metallurgical enterprises are crusher, dryer, mill, classifier, sintering machine, blast furnace, converter, open hearth furnace, steel rolling and so on. In addition, transportation equipment, the top, bottom, import and export of warehouses are dust sources that produce dust. Among them, metallurgical waste gas is the most difficult to treat because of its special working conditions of "humidity, corrosion and variability". The vast majority of metallurgical enterprises, due to financial constraints and conceptual reasons, invest less, which brings difficulties to waste gas treatment.

2 Several existing metallurgical dust removal technologies in China

In addition to all kinds of wet dust removal, electrostatic dust removal and cyclone dust removal, high-efficiency bag dust removal technology is still the mainstream of current application and the focus of this paper.

Working principle of bag dust removal technology and equipment in production process

1 pulse bag filter

The dust concentration in metallurgical plants is relatively high, generally above 600 g/m3, and the export can be as high as 1000 ~ 1200 g/m3. For such a high concentration of dust, the pulse bag filter is used for primary dust removal, which can not only meet the discharge requirements within 50g/m3 of the outlet, but also has simple system, low resistance and low energy consumption.

1) working principle of pulse bag filter

When the equipment works normally, dusty gas enters the ash hopper from the air inlet. Due to the rapid expansion of gas volume, some coarse dust particles fall into the ash hopper due to inertia or natural sedimentation, and most of the remaining dust particles rise with the airflow and enter the bag room. After being filtered by the filter bag, dust particles remain outside the filter bag, and the purified gas enters the upper box from the inside of the filter bag, and then is discharged into the atmosphere through the valve plate hole and the air outlet, thus achieving the purpose of dust removal. With the continuous filtration, the resistance of the dust collector is also rising. When the resistance reaches a certain value, the ash cleaning controller issues an ash cleaning command. First, the lift valve plate is closed to cut off the filtered air flow. Then, the dust removal controller sends a signal to the pulse solenoid valve. Because the pulse valve sends the high-pressure reverse airflow used for cleaning the dust into the bag, the filter bag expands rapidly and produces strong jitter, so that the dust outside the filter bag is shaken off, thus achieving the purpose of cleaning the dust.

2) Technical features

(1) does not need pre-dust removal equipment, and can treat flue gas with concentration as high as 1000 g/m3 at one time, with emission less than 50g/m3, and the process flow is simple;

(2) there is no need to blow a pipe in the bag room, so it is convenient to change bags outside the machine;

(3) The embedded elastic pocket has good sealing performance;

(4) The number of pulse valves is small, the ash cleaning intensity is high, and the action is rapid;

(5) The whole machine is automatically controlled by microcomputer, and all parameters can be easily adjusted, so as to achieve post-free operation;

(6) The service life of the filter bag is more than two years;

(7) It is easy to realize isolation and maintenance.

2 back-blowing bag filter

Back-blowing bag dust collector, internal filter type, requires 10 ~ 20s for each back-blowing in a room, and can only handle flue gas with normal concentration, so it is cheap.

1) working principle

2) Technical features

(1) Downdraft mode with inertial dust removal function;

(2) diamond-shaped filter bags are adopted, and the filtering area per unit volume is large;

(3) The filter material is thick and smooth, with high dust removal efficiency and easy dust removal;

(4) Exhaust and blowback are realized by the valve body;

(5) changing bags outside the machine, with few moving parts and convenient maintenance;

(6) Automatic control of special microcomputer instrument, convenient operation and parameter modification.

It is very important for metallurgical enterprises to realize clean production in the production process and finally control terminal management. At present, the environmental protection standards require that the emission concentration must be below tens of milligrams per standard cubic meter, and the smoke (or dust), sulfur dioxide, nitrogen oxides (calculated by NO2) and fluoride (calculated by total fluorine) produced by air pollution of production equipment have detailed regulations, and with the increase of environmental protection, the standards will only become stricter. China bag dust removal industry will further develop new technologies, new materials, new processes and new products to adapt to the growing environmental protection and civilized production of modern metallurgical industry in China.